Various medical procedures require the measurement of the temperature of a fluid, such as blood, flowing within a body. For example, to make thermodilution measurements, a bolus of cold liquid is injected into the right atrium or vena cava, and the resulting change in blood temperature is measured in the pulmonary artery. The temperature measurement is made by a thermistor which is carried by a thermodiultion catheter. U.S. Pat. Nos. 3,995,623; 4,105,022; and 4,329,994 show different techniques for mounting a thermistor on a catheter.
Thermodilution blood temperature measurements do not require that the thermistor have a very rapid response. However, for some medical procedures, such as the calculation of ejection fraction, it is necessary to measure changes in blood temperature as they occur. In this event, it is necessary or desirable that the thermistor measure blood temperature directly rather than the temperature of the catheter on which it is mounted. Specifically, the thermistor should follow the beat-to-beat blood temperature changes so that discrete steps in the temperature curve can be observed. Unfortunately, the patented constructions identified above prevent the thermistor from having an adequately rapid response.